Infusion therapy is a widely known therapy for patients who require medicaments to be delivered over some time period. Diabetic infusion pump therapy, which entails the purchase of an expensive pump that lasts for about three years, has possibly the largest population of outpatient infusion therapy. The initial cost of the pump is a high barrier to this type of therapy. From a user perspective, however, the overwhelming majority of patients who have used pumps prefer to remain with pumps for the rest of their lives. This is because infusion pumps, although more complex than syringes and pens, offer the advantages of continuous infusion of insulin, precision dosing and programmable delivery schedules. This results in closer glucose control and an improved feeling of wellness.
As patients on oral agents eventually move to insulin and their interest in intensive therapy increases, users typically look to insulin pumps. However, in addition to their high cost (roughly 8 to 10 times the daily cost of syringe therapy) and limited lifetime, insulin pumps represent relatively old technology and are cumbersome to use. Also, from a lifestyle standpoint, the tubing (known as the “infusion set”) that links the pump with the delivery site on the user's abdomen is very inconvenient and the pumps are relatively heavy, making carrying the pump a burden.
Therefore interest in better therapy is on the rise, accounting for the observed growth in pump therapy and increased number of daily injections. In this and similar infusion examples, what is needed to fully meet this increased interest is a form of insulin delivery or infusion that combines the best features of daily injection therapy (low cost and ease of use) with those of the insulin pump (continuous infusion and precision dosing) and that also avoids the disadvantages of each.
Several attempts have been made to provide ambulatory or “wearable” drug infusion devices that are low in cost and convenient to use. Some of these devices are intended to be partially or entirely disposable. In theory, devices of this type can provide many of the advantages of an infusion pump without the attendant cost and inconvenience. Unfortunately, however, many of these devices suffer from disadvantages including user discomfort (due to the gauge and/or length of injection needle used), compatibility and interaction between the substance being delivered and the materials used in the construction of the infusion device, and possible malfunctioning if not properly activated by the user (e.g., “wet” injections resulting from premature activation of the device). Long-term drug stability has also been an issue for these types of devices, and therefore a majority of drugs, when in liquid form must be refrigerated.
In order to combat the drug stability problem, storage-stability can be imparted to medicaments by placing them in a dry powder form. Techniques for doing this include freeze-drying, spray freeze-drying, lyophilization and the like. However, reconstitution of such medicaments has been difficult and involves many steps. Additionally, reconstituted liquids typically do not have the same properties as a liquid drug formulation, at least because bubbles may be formed during reconstitution.
Various methods to disrupt bubbles in reconstituted formulations have been attempted in the past. Most of these methods use application of ultrasonic energy. The ultrasonic effect is based on what is known as cavitation, i.e., cavities containing gas formed by sound waves. These cavities collide with each other forming larger cavities that then rise to the surface and dissipate. These methods require specialized and bulky equipment and power sources. Yet another drawback of cavitation is the momentary, yet intense, burst of heat generated as each bubble collapses. The heat generated can certainly destroy some active components or unstable drugs in the product. It would be desirable to have a method for removing bubbles from a reconstituted solution, which did not have such issues as high-energy input and heat generation. Other methods to reduce bubble formation that have been attempted are application of a high pressure. It is theorized that high pressures reduces bubble formation because the rate of bubble collapse is proportional to G, the gradient between external tension and bubble internal pressure. The higher external tension can shrink bubbles. With a decrease in diameter of the bubbles, the increased internal gas pressure forces the gas inside the bubble to dissolve, resulting in bubble collapse as the gas is forced into solution. Nevertheless, this approach also requires additional equipment safeguards and is not feasible for many applications due to either safety or cost concerns. Additionally, a bubble will form again after high pressure is removed, such as when the reconstituted product is drawn out of a pressured vial.
To date, however, there remains a need for a system for the administration of medicaments where the medicament is in a storage stable dry form, which can be readily reconstituted and directly administered via an infusion type device. Additionally, the reconstituted drug should have properties, which mimic the pre-mixed liquid formulation. Accordingly, a need exists for an alternative to current infusion devices, such as infusion pumps for insulin that further provides simplicity in manufacture and ease-of-use for both insulin and non-insulin applications.